Cut out window borders and application bars from screenshots automatically: note down some corner points (in Gimp), then use ImageMagick:
for f (*.png) { convert -crop 975x559+2+30 $f $f; }
Task done!
NB: This command replaces file contents. So when not
sure about the numbers, append some extension to it and view the
results first. Or, simply kepp the images in a git controlled
directory. That way, a simple git reset -- . will restore your
previous images if you added them in the first place.